Hi, > - If you have SSD drives you can mostly do what you want. I don't know > of anyone running huge varnish process that swap alot - but it _might_ > work. If you are, let me know.
Just wanted to add, there is someone running with a lot of storage with malloc/swap: * http://varnish-cache.org/trac/ticket/784 Wido On Fri, 2010-11-26 at 20:39 +0100, Per Buer wrote: > > > On Fri, Nov 26, 2010 at 4:41 PM, Angelo Höngens > <[email protected]> wrote: > Per wrote in his survey result: "62% use -s file, which I find > somewhat surprising. -s file doesn't really perform that well > under pressure on rotating hard drives due to some changes in > recent Linux and FreeBSD kernels." > > But does anyone have a link to (or write up) some explanation > for dummies on cache file types? I know there's 'file' and > 'malloc', but I don't know the difference or the pros and > cons. > > > In Varnish 1.0 we had -s file and everything was fine. People where > using Varnish on Linux 2.6.9 (and thereabout) and FreeBSD6. Then came > 2.6.18 with RHEL5 and some other Linux distros and Varnish started > behaving a bit strange. The IO pressure had increased and we saw load > skyrocket with Varnish being stuck IO sleep a lot of the time, waiting > for writes to finish. Then FreeBSD7 came out and showed the > same behavior. Obviously the kernel developers of the world where > ganging up on us. > > > Alterations in vm behavior are difficult things to track down and the > chances of changing the behavior back might be slim - Varnish being > something of an oddball doing crazy stuff like mmaping several > gigabytes and accessing it in a random fasion (and most of them saying > things like "Wow, that actually works?" when hearing what we do). > > > Anyway, Poul came up with -s malloc, which just allocates slabs of > ordinary memory and stores everything there. Since ordinary memory > isn't backed by disk a write to memory doesn't trigger a write to disk > so there are no sync disk writes to slow us down. On the flip side - > at least on Linux, if your data set doesn't dit in memory - the moment > you start to actively use your swapping space things grind to a halt. > FreeBSD seems to cope better with programs being larger then the > amount of memory. > > > Several people are running high traffic sites with -s file backed by > SSD. That seem to perform very well on Linux. Our main FreeBSD user, > Anders N, uses -s malloc so I don't know much about how -s file on > FreeBSD anymore. > > > So, to sum up: > - If you have SSD drives you can mostly do what you want. I don't > know of anyone running huge varnish process that swap alot - but it > _might_ work. If you are, let me know. > - If your varnish process doesn't write that much you're probably in > the clear no matter what you'll do. > - If you have a small data set that fits neatly in memory, use -s > malloc. > - If you you have a large data set that doesn't fit in memory you > have to get SSD drives. > > > Oh, and at least on Linux there are a bunch of tunables that might > alter or even rectify some of the misbehavior we've seen. > > > > > I should clean this up, get some tests done and write it up > somewhere. > -- > Per Buer, Varnish Software > Phone: +47 21 98 92 61 / Mobile: +47 958 39 117 / skype: per.buer > _______________________________________________ > varnish-misc mailing list > [email protected] > http://lists.varnish-cache.org/mailman/listinfo/varnish-misc _______________________________________________ varnish-misc mailing list [email protected] http://lists.varnish-cache.org/mailman/listinfo/varnish-misc
